1. Field of the Invention
The present invention relates to a polishing apparatus for a magnetic head and a method therefor, for polishing a polished article composed of an array of plural magnetic heads, and more particularly to an apparatus and a method for finishing a polished surface into a smoothly curved convex shape (hereinafter called crown shape).
2. Related Background Art
In the batch-based manufacturing process for a thin film magnetic head for use in a disk drive device for computers, there is conventionally included a step of polishing a bar-shaped ceramic (ceramic bar), on which plural conversion units including a thin magnetic film are aligned in an array on the surface, together with such conversion units thereby finishing the throat height of the gap (height of the gap portion) of each conversion unit into an appropriate value. The ceramic bar is cut off into individual conversion unit in a subsequent step, and each cut-off portion constitutes a part of the magnetic head for use in the magnetic disk drive device. In the use of such magnetic head in the magnetic disk drive device, the ceramic portion constitutes a slider which floats on the magnetic disk by the air pressure generated by the rotation of the magnetic disk, and the conversion unit including the thin magnetic film constitutes a head core for recording and/or reproducing the magnetic signal of the disk.
In the above-mentioned conversion unit, there are formed an induction magnetic converting element of signal writing and a magneto resistive (MR) element for signal reading. Also the throat height mentioned above means, in such head core, the length (height) of a portion where the end portions of the two magnetic poles for writing or reading the magnetic signal are mutually opposed with a very small gap therebetween. The magnitude of such throat height has to be maintained at a predetermined value in order to enable appropriate recording and reading of the signal, and a high precision is therefore required for the polishing work.
There have already been proposed apparatus for high precision polishing of the magnetic heads in the form of the above-described ceramic bar (for example the U.S. Pat. No. 5,620,356 etc.). Also the present applicant proposed certain apparatus and methods (for example the Japanese Patent Application No. 11-162799 etc.).
As briefly explained in the foregoing, in the operated state of the disk drive device, the chip member (consisting of slider and head core) at the end of the magnetic head supported by a suspension is maintained in a floating state separate by several hundredths of a micron from the disk, by the pressure of an air flow generated by the high speed revolution of the magnetic disk. The chip member in the floating state has to be constantly maintained in a stable position, in order to achieve accurate information recording and reproduction to and from the magnetic disk.
For this purpose, in certain magnetic heads, the surface, opposed to the magnetic disk, of the chip member positioned at the end of the head is given a rounded or curved shape, thereby suppressing the influence on the floating state of the chip member, resulting from the change in the air flow between the internal and external portions of the magnetic disk.
In order to form such curved shape (hereinafter called crown working or crowning) in a batch process, a ceramic bar bearing plural conversion units including a magnetic thin film is at first polished for obtaining a desired throat height as explained in the foregoing, and is then subjected to a crown working on the same surface for obtaining a desired curved surface shape.
The above-mentioned crown working is possible with the apparatus proposed by the present applicant in the above-mentioned Japanese Patent Application No. 11-162799. This apparatus is provided with a horizontally positioned and rotated polishing table, and a polishing head for supporting a work to be polished (namely ceramic bar bearing plural conversion units) and maintaining such work in a desired position in contact with the polishing table thereby executing polishing of the work. The polishing head is mounted on a mounting frame which is movable in the horizontal direction and in the vertical direction. The polishing head is supported, so as to be rotatable in the horizontal plane, by an annular bearing on the mounting frame.
The polishing head of the apparatus proposed in the Japanese Patent Application No. 11-162799 is provided, at the bottom face thereof, with an adjusting ring. During the polishing operation, the adjusting ring is in contact with the polishing plane, which is the upper surface of the polishing table, thereby defining a reference plane for the position of the polishing head. The polishing head is further provided with an inclining unit, capable of inclining a reference system based on the adjusting ring (namely a system consisting of components fixed to the adjusting ring) by a desired angle about a predetermined horizontal axis. Thus the inclining unit can incline the reference system, including the adjusting ring, by a desired angle with respect to the vertical direction. The inclining operation of the inclining unit is achieved by a motor.
The apparatus is further provided with means adapted, in polishing the polished surface of the ceramic bar constituting the work, for adjusting the bending or torsion of the work, thereby adjusting the horizontal balance of the polished amount. More specifically, the pressure of the work to the polishing table is adjusted in arbitrary plural points in the longitudinal direction of the work, thereby correcting the torsion etc. of the work and adjusting the polished amount.
In the above-described apparatus, in the ordinary polishing operation for setting the throat height to the desired value, the inclination angle of the inclining unit is fixed throughout the polishing process of a work. Also in such polishing process, the polishing plane of the polishing table of the apparatus is maintained perpendicular to the work, whereby the polished surface thereof is polished flat.
Also with such apparatus it is theoretically possible to form a crown on the polished surface, utilizing the inclining unit provided in the apparatus. More specifically, the polished surface can be finished into a rounded shape by executing the polishing operation by gradually and continuously changing the inclining angle of the inclining unit. However, the crown working employing such apparatus is difficult to provide a smooth curved surface of a desired curvature, resulting in a significant fluctuation in the obtained curved surface and requiring complex control of the apparatus in such polishing operation.
For this reason, the crown working of the polished surface of the ceramic bar work is also executed an apparatus provided with a polishing table having a spherical-shaped polishing plane. In an example of such apparatus, the ceramic bar work is attached on a rubber sheet adhered to an end face of a rod-shaped jig and is pressed to the polishing table by means of such jig and the polishing operation is executed under the control of the total pressing pressure. In another example, the ceramic bar work is attached to a jig of square rod shape through rubber and the polishing operation is executed by pressing the polishing head, including the jig and the work, by the weight thereof to the polishing plane.
In summary, the above-described conventional apparatus is incapable of crown working of the magnetic head with a high precision. Also the apparatus disclosed in the Japanese Patent Application No. 11-162799 is impractical for such crown working, because the smoothly curved surface is practically difficult to obtain as the inclination of the inclining unit has to be changed gradually under complex control.
Also in the apparatus provided with the polishing table having the spherical polishing plane, the worked shape obtained by polishing is conventionally controlled by the pressing weight of the work to the polishing table and the working time, and the polished amount cannot be controlled precisely for example because of a change in the polishing rate resulting from the fatigue of the polishing slurry.
In consideration of the foregoing, the object of the present invention is to provide a polishing apparatus and a polishing method, capable of high-precision crown working of the magnetic heads.
The above-mentioned object can be attained, according to the present invention, by a polishing apparatus for polishing a polished work bearing a plurality of magnetic heads, the apparatus comprising a rotated polishing table having a polishing plane constituting a part of a spherical plane of a predetermined radius of curvature, a frame for mounting a polishing head, rendered movable with respect to the polishing plane, and a polishing head supported by the polishing head mounting frame, wherein the polishing head includes a jig for supporting the polished work through the elastic member, a back plate on which the jig is mounted, an elevator unit capable of ascending and descending integrally with the back plate with respect to the polishing plane and supporting the back plate in rotatable manner about the supporting point and in a plane parallel to the direction of ascending and descending, plural correcting actuator means for pressing the back plate to the polishing plane, measuring means for measuring the characteristics of the magnetic head formed on the polished work, and control means for controlling the pressing forces of the plural correcting actuator means according to the measured value.
For attaining the above-mentioned object, there is preferred a configuration in which the elevator unit is supported by an inclining unit and the direction of ascending and descending is inclined by inclining the inclining unit by inclining unit drive means. Also the polishing head is preferably mounted in rotatable manner on the polishing head mounting means. It is further preferred that the apparatus comprises polishing head rocking means and that the polishing head rocking means causes the polishing head to execute a reciprocating rotary motion within a predetermined angular range.
Also the plural correcting actuator means are preferably composed of three low-friction cylinders, and the pressing portions on the back plate by the low-friction cylinders are preferably positioned on the supporting point of the back plate and on both sides of the aforementioned supporting point in the longitudinal direction of the back plate.
Furthermore, the aforementioned predetermined radius of curvature of the polishing plane is preferably within a range from 4 to 6 meters, and the elastic member is preferably composed principally of rubber. Furthermore, the polished work is preferably provided, on a surface opposed to the polishing plane, with plural grooves perpendicular to the longitudinal direction, and the measured characteristics of the magnetic head is preferably magnetic resistivity.
The above-mentioned object can also be attained, according to the present invention, by a polishing method for polishing a polished work bearing a plurality of magnetic heads, the method comprising a step of causing a jig to support the polished work through an elastic member, a step of moving the jig to a predetermined position relative to a rotated polishing table having a polishing plane constituting a part of a spherical plane of a predetermined radius of curvature, a step of rotatably supporting the jig in a plane substantially perpendicular to the polishing plane and descending the jig onto the polishing plane, and a step of pressing the polished work to the polishing plane through the jig thereby polishing the polished work, wherein the jig can be pressed toward the polishing plane in plural points other than the rotatably supporting point, and the measurement of the polished amount based on the measurement of characteristics of the magnetic head and the adjustment of the pressing forces at the supporting points and the plural points based on the results of measurement are repeated plural times in the polishing step.
Also for attaining the aforementioned object, it is preferred, in the step of causing the jig to support the polished work, to adjust the direction of descent of the jig toward the polishing plane. Also in the polishing step, the jig preferably executes a reciprocating rotary motion within a predetermined angular range about the supporting point where the jig is rotatably supported and substantially parallel to the polishing plane. Also the pressing at the supporting point and the plural points is preferably executed by low-friction cylinders, and the plural pressing points are preferably positioned on both sides of the supporting points in the longitudinal direction of the jig.
Furthermore, the aforementioned predetermined radius of curvature of the polishing plane is preferably within a range from 4 to 6 meters, and the elastic member is preferably composed principally of rubber. Furthermore, the polished work, being supported by the jig through the elastic member, is preferably provided, on a surface opposed to the polishing plane, with plural grooves perpendicular to the longitudinal direction, and the measured characteristics of the magnetic head is preferably magnetic resistivity.